/* Add stylesheet to page */

var presStyle  = document.createElement('link');
presStyle.type = 'text/css';
presStyle.rel  = 'stylesheet';
presStyle.href = '/presentation.css';
document.head.appendChild(presStyle);

/* Print button */

const printBtn = document.getElementById('printBtn');

printBtn.addEventListener('click', function() {
	window.print();
});

/* Next and previous buttons */

const prevSlideBtn = document.getElementById('prevSlideBtn');
const nextSlideBtn = document.getElementById('nextSlideBtn');

const slides = document.getElementsByClassName('slide');
var slideIndex = 0;

  // Shows the "slideIndex + mod" numbered slide
function showSlide(mod) {
	slides[slideIndex].classList.remove('absolute-slide');
	slideIndex = (slides.length + slideIndex + mod) % slides.length;
	slides[slideIndex].classList.add('absolute-slide');
}

prevSlideBtn.addEventListener('click', function() {
	showSlide(-1);
});

nextSlideBtn.addEventListener('click', function() {
	showSlide(+1);
});

/* Present button */

const presentCont = document.getElementById('presentCont');
const presentBtn = document.getElementById('presentBtn');
const articleBtn = document.getElementById('articleBtn');

var presenting = false;
var pageY = 0;
var pageX = 0;

presentBtn.addEventListener('click', function() {
	// Hide the whole page
	document.body.classList.toggle('invisible');
	document.body.classList.toggle('no-overflow');
	// Fix background color
	document.body.classList.toggle('body-bg-color');
	// Show the slide controller
	presentCont.classList.toggle('absolute-cont');
	prevSlideBtn.classList.toggle('nodisplay');
	nextSlideBtn.classList.toggle('nodisplay');
	articleBtn.classList.toggle('nodisplay');
	printBtn.classList.toggle('nodisplay');
	// Show the first slide
	slides[slideIndex].classList.toggle('absolute-slide');
	// Alignment of presentation to screen
	if (presenting) {
		window.scrollTo(pageX, pageY);
	}
	else {
		pageY = window.scrollY; pageX = window.scrollX;
		window.scrollTo(0, 0);
	}

	presenting = !presenting;
});

/* Show as article button */

articleBtn.addEventListener('click', function() {
	printBtn.classList.toggle('nodisplay');
	presentBtn.classList.toggle('nodisplay');
	// Toggle presentation.css
	document.styleSheets.item(3).disabled = !document.styleSheets.item(3).disabled;
});

/* Keyboard controls */

document.addEventListener('keydown', function (e) {
	switch (e.code) {
		// Previous slide
		case 'Backspace': case 'PageUp':
		case 'ArrowLeft': case 'ArrowUp':
			showSlide(-1);
			break;
		// Next slide
		case 'Space': case 'Enter': case 'PageDown':
		case 'ArrowRight': case 'ArrowDown':
			showSlide(+1);
			break;
		// Start (toggle) presenting
		case 'KeyP': case 'KeyT':
			presentBtn.click();
			break;
		// Exit presentation
		case 'Escape':
			if (presenting) presentBtn.click();
			break;
		// Go to first slide
		case 'Home':
			if (presenting) showSlide(-slideIndex);
			break;
		// Go to last slide
		case 'End':
			if (presenting) showSlide(-slideIndex -1);
			break;
	}
});